Efficiency Improvement in Nonprime Crystalline Silicon Solar Cells by Chemical Isolation of Shunts Under Front Metallization

Yield loss due to the breakage and production of nonprime or off-spec cells in industrially produced crystalline silicon-based solar cells is around 1-2%. Nonprime cells identified based on their electrical properties are rejected after quality inspection. The cells that are rejected can be classified as nonprime for many reasons, such as poor edge isolation, presence of conductive paths through p-n junctions formed by print paste stains, paste-filled microcracks, inclusions, nonuniform emitter, and nonuniform antireflective coatings. Development of efficient and economically feasible repair methods for the repowering of nonprime cells will increase the overall yield of the solar cell industry and reduce costs. To isolate severe shunts under front metallization, we developed a two-step chemical etching process to remove front metallization and emitter. Removal of front metallization and emitter yielded the best isolation of shunts. Shunt isolation and efficiency gain achieved by the chemical etching process has been demonstrated on both mono- and multicrystalline silicon solar cells.